Q: A well-known technique for preventing wood from splitting while it is being nailed is to blunt the nail by tapping the sharp end with a hammer while holding the head against a firm surface. This lowers the incidence of splitting considerably. But why should a blunt nail stop wood splitting? You would expect the reverse.
A: A pointed nail when hammered, progresses through a piece of wood by forcing the fibres apart. This obviously causes stress in the fibres and if near the end or edge of your piece of wood, will cause the fibres to give way under stress. A nail with its point blunted tears through some of the fibres rather than forcing its way between them, reducing sideways stress and subsequent splitting.
You might be tempted to enquire why manufacturers no longer make nails with ends that are chisel-shaped (there used to be some flooring and roofing nails that were vaguely chisel-shaped)? Unfortunately, when driven into a fibrous material, a chisel-ended nail always tries to take the path of least resistance and twists itself through 90 degrees, so the chisel end no longer cuts the fibres, but acts as a wedge between them in much the same way as a pointed nail.
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In theory this could be overcome by producing a very oval nail with a chisel end at a right angle to the oval. The exaggerated oval section would counteract the twisting motion of the chisel end. However, I imagine the cost of producing this nail would be high in relation to its standard wire or oval brethren.
The action of nails in wood is quite complex but, to put it simply, a nail that levers its way through the wood fibres will hold better than one that cuts the fibres, for obvious reasons.
A: This principle is the key to why many floorboards in modern houses creak so soon after being laid. Today, oval nails with a sharp point are often used because they are cheaper. However, floorboards used to be laid using iron cut nails which had a flat point. The flat point reduced the pressure around the buried nail and so lessened the chance of traffic over the board working it loose.